Assessing the role of anoxia as an extinction driver in shallow marine basins during the Permian–Triassic mass extinction.

The Permian–Triassic mass extinction led to the loss of 80-90% of marine species making it the most catastrophic extinction of the Phanerozoic. The Permian-Triassic transition is characterized by a major clime warming event, major environmental upheaval and a high magnitude mass extinction event. The associated expansion of oxygen minimum zones, even into shallow waters, is commonly considered as a global driver of this extinction. However, while the intensification of deep-water anoxia has been demonstrated utilising U isotopes at multiple sites globally, recent studies have shown increasing evidence for spatial and temporal variability in shallow marine redox conditions across the Permian–Triassic transition. This highlights the need to constrain local redox conditions for shallow marine basins to determine if they were affected by anoxia and to link local redox changes, if any, back to the timing of the extinction event. Here, we present redox sensitive element (Re, V, U and Mo) and rare earth elements and yttrium (REY) data from three shallow marine basins, located in the western Paleotethys (Dolomites, Italy), Neotethys (Antalya, Türkiye), and the Barents Sea (Svalbard, Norway) to understand the role of oxygen availability as an extinction driver in different environmental and latitudinal settings. At all three sites, redox sensitive metal enrichments were observed before the onset of the extinction, suggesting deoxygenation, potentially creating anoxic conditions. However, these enrichments appear to be lithology- rather than redox-driven in the Svalbard section and are not persistent within the Dolomites sections, suggesting only episodic deoxygenation. Furthermore, the Dolomites and Antalya sections generally display lower metal enrichments starting at the extinction onset, suggesting lower oxygenation before the extinction than during it. Seawater-like REY patterns were not preserved at all sections, however, all three localities included sections characterized by negative Ce anomalies typical for oxic seawater conditions during the extinction. This suggests that anoxia was not a driving extinction factor in these shallow marine ecosystems, indicating other extinction mechanisms should be considered.